In food and beverage packaging, metal cans and glass bottles were traditionally the preferred packages. With the introduction of polypropylene (PP) and ethylene vinyl alcohol copolymer (EVOH) multi-layer containers, PP/EVOH containers, and poly(ethylene terephthalate) PET containers in the 1980s, a portion of the metal-based and glass-based packages were replaced by plastics-based packages.
The shelf life of a plastic package is determined by the amount of oxygen that permeates into the package. A container made from amorphous poly(ethylene terephthalate) (APET) typically has a shelf life of three to six months. A container made from crystalline poly(ethylene terephthalate) (CPET) typically has a shelf life of five to ten months. Because both APET and CPET containers have a PET recycling code (“1”), which is considered most environmental friendly due to the successful development of recycling infrastructure over the years; it would be desirable to improve the oxygen barrier of these materials so they can be used extensively in packaging for food and other oxygen-sensitive products. Many unsuccessful attempts have been made at incorporating an effective oxygen scavenger into the walls of PET containers such that the container has zero or negative oxygen permeation to compete with the metal-based and glass-based packages.
Not only do commercially available oxygen scavenging containers fall short of achieving zero or negative oxygen permeation, but they have several other drawbacks. For instance, many articles of active packaging suffer from two oxygen absorption initiation problems: (1) short or no induction period and (2) long or infinite induction period. When the induction period is too short, it allows for ambient oxygen absorption during inventory before the container is filled (i.e., before oxygen absorption is desired). On the other hand, when the induction period is too long, they require some sort of triggering agent, such as ultraviolet light or water, to begin scavenging. A further disadvantage of these containers is that such materials may require thick sidewalls, which adds to cost.
Many commercially available oxygen-scavenging containers begin to scavenge oxygen immediately. Without an incubation period, the expensive oxygen scavenger is wasted during the inventory period. It is common in the industry for containers to be in transportation from supplier to user for a couple months. It is therefore desirable to keep the container from scavenging oxygen during inventory and start oxygen scavenging immediately when the container is filled with product.
It would be beneficial to develop a plastics-based package for food or beverages with less oxygen permeation and more controlled oxygen scavenging. There remains a need for packaging materials that perform these feats in a more efficient and cost-effective manner. It would be beneficial to improve the shelf life of containers made specifically from PET-based materials. It would be further beneficial to discover efficient methods of manufacturing such containers.
There is no admission that the background art disclosed in this section legally constitutes prior art.